1. Field of the Invention
The present invention relates to an optical disc apparatus for recording information on, and erasing recorded information from, a rewritable optical disc having a power calibration area for optimum recording power calibration.
2. Description of the Related Art
A rewritable optical disc such as a DVD-RW (Rewritable) as well as a write-once optical disc such as a DVD (Digital Versatile Disc)-R (Recordable) has a test recording or writing area which is referred to as power calibration area (hereafter simply as “PCA”). An optimum recording power can be obtained by test recording, more specifically recording test data in the PCA with different powers of laser beam, and reproducing the recorded test data, which can be referred to as optimum recording power calibration or control (hereafter simply as “OPC”). In the case of a rewritable optical disc such as a DVD-RW, the data recorded in the PCA by the test recording can be erased, in contrast to the case of a write-once optical disc. Thus, if the OPC is repeated to cause the PCA to run out of free space (unused or usable area) for further test recording, it is possible to erase the data recorded by test recordings in the PCA so as to create a free space, thereby enabling further OPC.
When the PCA runs out of free space due to the repetition of the OPC, data recorded in the PCA by the test recording is erased by a laser beam (erase laser) using a constant power (DC voltage) which is not in pulse form, so as to restore a used area of the PCA back to a usable area. Because of the use of DC voltage, the operation to erase the data in the used area in the PCA is called “DC erase”. Here, the power of the laser beam for performing the DC erase (DC erase laser power) is also set to be optimum based on the optimum recording laser power obtained using the PCA. So, normally, a portion of the PCA is kept unused to enable or carry out the OPC at least one time in the case where test data are repeatedly recorded in the PCA.
There is a technical standard for the process of repeatedly recording test data in PCA of a rewritable optical disc. An optical disc apparatus of a first type uses this technical standard. The technical standard recommends using the PCA continuously from an outer radial position toward an inner radial position of the optical disc. Based on this recommendation, an innermost end of an area having test data recorded therein (i.e. used area) in PCA can be determined in the following manner. That is, first, an optical pickup in the first type of optical disc apparatus is moved to seek from a radially innermost end of PCA to radially outward of the rewritable optical disc in order to detect a free space (usable area) in the PCA when starting OPC. Note that in the present specification, the term “radially” is used to mean “in a direction along a radius of an optical disc”.
During the seek movement, the optical pickup receives a reflected laser beam which may contain a reproduction signal. The first type of optical disc apparatus determines that the position of the optical pickup at an address in the PCA, at the time of first detecting the reproduction signal after detecting a free space in the PCA, is the radially innermost end of the used area in the PCA, thereby identifying the usable area (free space) in the PCA. Note in this connection that normally the PCA has an area called RMA (Recording Management Area) to record an address of an area of the last performed OPC. By reading the address recorded in the RMA, the address of the used area can be obtained. However, the address recorded in the RMA is not always renewed as a new address. Thus, in order to securely detect a usable area in the PCA, the above-described manner of identifying the usable area is generally used.
Once the usable area in the PCA of the rewritable optical disc is identified, the first type of optical disc apparatus performs OPC at an outermost position in the usable area (i.e. position neighboring the used area) in a manner provided by the above-described technical standard. If only about a portion of the PCA is kept unused as the usable area to enable or carry out the OPC just one time (i.e. if the PCA is almost completely used up), the optical disc apparatus performs the OPC in the usable area so as to obtain an optimum recording power (laser power). Using the thus obtained optimum recording power, and based on a known predetermined relationship between optimum recording power and optimum erase (DC erase) power, the optical disc apparatus obtains an optimum erase power (laser power), and performs DC erase based on the thus obtained optimum erase power. By subjecting the entire area, except e.g. recording management area, of the PCA (hereafter such entire area being referred to often as “entire substantial area”) to the DC erase (such), the entire substantial area of the PCA is restored to a usable area spanning from a radially innermost end to a radially outer end of the PCA. For starting e.g. recording on the optical disc thereafter, the first type of optical disc apparatus first operates its optical pickup to detect the usable area thus restored in the PCA from the radially innermost end of the PCA in the optical disc, and to seek radially outwardly therefrom, so as to use the usable area (free space) of the PCA for OPC.
On the other hand, there is a known technology in which after an entire area of PCA in a rewritable optical disc is once completely used up, a portion of the PCA to be used for a subsequent OPC is randomly set. A second type of optical disc apparatus uses this technology. In the second type of optical disc apparatus, there is a possibility that a certain area of the PCA is used by far more frequently than the other of the PCA. Thus, an improved process has been developed for the second type of optical disc apparatus in which, after each test recording in a then free space of the PCA, a portion of the PCA from the front end of the each test recording area to a certain inner position of the PCA is subjected to erasure to form or create a new free space of the PCA. By retrieving and setting this new free space for a subsequent test recording, a subsequent test recording can be easily performed in the second type of optical disc apparatus, even after the entire area of the PCA is once completely used up (refer to e.g. Japanese Laid-open Patent Publication 2003-272157).
As apparent from the foregoing, the first and second types of optical disc apparatus are different from each other with respect e.g. to the process of recording test data in PCA, the process of detecting a usable area in the PCA, and the process of performing DC erase when the PCA is completely or almost completely used up. However, a rewritable optical disc can be mounted on either of the two different types of optical disc apparatus. When one optical disc is actually mounted for use on the two different types of optical disc apparatus, which are different from each other particularly in the process of DC erase, the following problem may occur.
Assume that a rewritable optical disc is first mounted on and used by an optical disc apparatus of the second type so as to form a usable area in PCA of the optical disc at a random position in the PCA (e.g. an intermediate position “ap” as shown in later described FIG. 5A). Further assume that the optical disc is thereafter mounted on an optical disc apparatus of the first type so as to subject the optical disc to recording or erasure. Under these assumptions, the first type of optical disc apparatus cannot detect the usable area formed by the second type of optical disc apparatus, resulting in detection failure, because the PCA of the optical disc does not have a usable area (free space) on a radially inner portion of the PCA, more specifically does not have a usable area spanning from a radially innermost end of the PCA up to the front end of the usable area formed by the second type of optical disc apparatus. Thus, the first type of optical disc apparatus cannot perform OPC, either. This problem needs to be solved.
Besides, it is to be noted that in connection with appropriate erasure of data on a rewritable optical disc, there are technologies to control the erase power. For example, a technology is known to prevent data recorded by test recording from being left unerased after DC erase (refer to e.g. Japanese Laid-open Patent Publication Hei 10-134389), in which the DC erase power is set to have a more appropriate value based on a signal reproduced from PCA after the DC erase. Furthermore, a technology is known to obtain an appropriate value of a laser output for erasure to be used for a rewritable optical disc (refer to e.g. Japanese Laid-open Patent Publication 2001-229563), in which the laser output irradiated onto a portion of the optical disc is varied, and an average reflectivity of the irradiated portion of the optical disc is measured, so as to determine an optimum laser output for erasure. However, these technologies are unable to solve the above-described problem.